Loma Prieta Mine (Commercial Mine; Copper Glance Mine; Patented claims MS 3425; Copper Hill Mine [?]; Copper Basin group [in part]), Copper Basin District, Sierra Prieta Mts, Yavapai Co., Arizona, USA
Latitude: 34°29'23"N
Longitude: 112°34'59"W
‡Ref.: Tovote, W. (1917) Loma Prieta Mines (unpublished report).
Yavapai Magazine (1918) April, 1918 (Sharlot Hall Museum, Prescott, AZ).
Anderson, C.A. (1943) Report on a Brief Examination of the Molybdenite Prospects at Copper Basin, Yavapai County, Arizona (unpublished report).
Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 25.
Johnston, W.P. (1955) Copper Basin Deposits, Ph.D. thesis, University of Utah, 130pp. (unpublished).
Johnston, W.P. and Lowell (1961) Geology and Ore Deposits of Mineralized Breccia Pipes in the Copper Basin, Arizona. Economic Geology: 56: 916-940.
Kirkemo, H., et al (1965), Investigations of Molybdenum Deposits in the Conterminous United States 1942-60, Contributions to Economic Geology, USGS Bull. 1182-E: E17, E26-E30.
USGS & Arizona Bureau of Mines, and U.S. Bureau of Reclamation (1969), Mineral and Water Resources of Arizona, Arizona Bureau of Mines Bull. 180 (USGS Bull.871): 149.
State of Arizona Department of Mineral Resources, Proven Copper Reserves in Arizona (1978): Table XXII.
Phelps Dodge Annual Report (1974).
Christman, Jerry (1978) Copper Basin District, M.S. thesis, University of Arizona, 78 pp. (unpublished).
Hicks, C.J. (1979), Molybdenum occurrences in Arizona, Arizona Department of Mineral Resources Min. Report #3: 26.
Southwest Pay Dirt (1987) August, 1987: 16A.
Southwest Pay Dirt (1989) April, 1989: 7A.
Southwest Pay Dirt (1990) December, 1990: 7A.
Niemuth, N.J. & K.A. Phillips (1992), Copper Oxide Resources, Arizona Department of Mines & Mineral Resources Open File Rept. 92-10: 17 (Table 1).
Sawyer, M.B., Gurmendi, A.C., Daley, M.R., and Howell, S.B. (1992) Principal Deposits of Strategic and Critical Minerals in Arizona, U.S. Bureau of Mines Special Publication, 334 pp.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd.ed.: 302.
Phelps Dodge Corp. Annual Report (1995): 23.
U.S. Bureau of Mines - Arizona Bureau of Geology and Mining Technology file data.
USGS Wilhoit Quadrangle map.
Arizona Department of Mineral Resources Commercial Mine file.
Arizona Department of Mineral Resources Loma Prieta Mine file.
U.S. Bureau of Land Management Mining District Sheet 268.
MRDS database Dep. ID #10048060, MRDS ID #M800029; and Dep. ID #10072137, MRDS ID #W016056; and, Dep. ID #10234396, MAS ID #0040250529;
and, Dep. ID #10027661, MRDS ID #M003742; and Dep. ID #10234691, MAS ID #0040251306; and, Dep. ID #10259519, MAS ID #0040250015.
A former underground Cu-Ag-Au-Pb-Mo-Zn mine located on the boundary of secs. 20 & 21 (in the SW¼ sec. 21), T.13N., R.3W., ½ mile east of the Copper Hill deposit (Wilhoit 7.5 minute topo map). Discovered in 1885 by Dan O'Carroll. Owned by Mrs. Sophia Smoot, Prescott (1943); and, the Loma Prieta Mines Co. (1916-1918 timeframe). Owned by the Phelps Dodge Corp., and under lease to F.S. Schemmer (circa 1943). Discovered 1890. Produced 1906-1968 and produced 1917-1918. Consists of patented claims: 485, 486, 487, 488, 489, 491, 510, 511, 512, 513, 514, 515, 516, and 518. Claims extend into the SE¼SE¼SE¼ of sec. 17, S½SW¼ of sec. 16, the N½ of sec. 28, and the N½NE¼NE¼ of sec. 29 & 21. Claims extend into RRC 59B.
Mineralization is a breccia pipe about 600 feet in diameter at the surface with a pipe-like, cylindrical, vertical ore body. Ore control was ore localized in breccia pipes and along late stage dikes along with disseminated ore. Alteration was sericitization and argillization. Ore concentration was oxidation and enrichment at near surface. Alteration was seritization and clay. An associated rock unit is the Copper Basin Stock.
Area structures include the Copper Basin Stock elongate NNE-SSW, faults N20-26W and N20-30E. Foliation in Precambrian rocks = N20E to N20W, with a steep dip west. Breccia around older quartz latite porphyry. The prevailing rock is fine- to medium-grained quartz diorite, deeply weathered in part and locally mineralized along joints with pyrite. Dikes of rhyolite and quartz diorite porphyry intrude the quartz diorite.
In the vicinity of the mine the quartz diorite has been brecciated, altered by hydrothermal activity, and cemented by quartz containing sulfide minerals, which are oxidized at the surface to limonite. The general elliptical horizontal outline of the breccia and the heterogeneity indicate that the mineralized breccia is part of a breccia pipe 250 feet in diameter.
The quartz cementing the breccia fragments is of two types. The more common type is white, contains coarse feldspar crystals, and has vugs lined with dolomite. The less common type of cementing quartz is dense and flinty, and its fuzzy margins agaianst the quartz diorite suggest some replacement of the fragments. In both types of quartz sulfide minerals, pyrite and chalcopyrite, form coarse blobs and bunches that are generally confined to the center of the cementing veins. Molybdenite finely divided and forms narrow veinlets either at the marghin ofn the veins or crosscutting the quartz. In a few places, the quartz veins are brecciated and cemented by younger, finely-divided molybdenite.
Development work occurred during the period 1916-18. The underground workings comprise the 46, 75, 150, and 400 levels and avertical shaft 414 feet deep. Workings include shafts, adits, drifts and crosscuts, all within limits of the breccia pipe. Incomplete production records to 1955 show that more than 150,000 tons of high-silica copper ore was produced.
Mineral List
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